Abstract: In lab conditions, we conducted a series of experiments to investigate the responses of fluorescence parameters(maximum quantum yield, effective quantum yield and the ratio of active Chl a to total Chl a) of photosynthetic system Ⅱ to the population growth of Prorocentrum donghaiense. The results showed that when the external nutrient was sufficient, the population growth of P. donghaiense exhibited distinct lag and exponential phases. The fluorescence parameters steadily increased in the lag phase, and kept constantly high values before reaching the inflection point. When the external nutrient was insufficient, the population growth showed the distinct lag phase; however, the exponential phase was shortened. The fluorescence parameters(effective quantum yield and the ratio of active Chl a to total Chl a) showed no significant changing pattern in the lag phase, but an overall increasing trend was observed during the growth period. Our results suggested that the fluorescence parameters of P.donghaiense can be affected by the different growth pattern and external nutrient status.